In general, permanent magnet motors, such as a polyphase brushless DC motor, have some saliency associated with them. Such saliency in a motor tend to cause self-inductance of a phase winding of the motor to arise as a function of the position of a rotor of the motor, which tends to cause mutual coupling between the energized phases of the motor and varies as a function of the position of the rotor. These variations and mutual couplings tend to cause noise to appear on detected back electromotive force signals that is observed from the phase windings.
It is may therefore be advantageous to attenuate this noise to obtain more accurate back electromotive force signals.